1. Field of the Invention
The present invention relates to a fuel cell that generates electricity by using an electrochemical reaction which is used for, for example, an electric vehicle.
2. Description of the Related Art
A fuel cell is, as well known, a device in which a pair of electrodes are made to be brought into contact with each other through an electrolyte, a fuel is supplied to one of the electrodes, an oxidant is supplied to the other electrode, and oxidation of the fuel is made to take place electrochemically in the cell, so that chemical energy is directly converted into electrical energy.
Fuel cells have several types according to the electrolyte. In recent years, as a fuel cell capable of obtaining high output, attention has been paid to a solid polymer type fuel cell which uses a solid polymer electrolyte film as an electrolyte. For example, when a hydrogen gas as a fuel is supplied to an anode, an air as an oxidant is supplied to a cathode, and an electric current is extracted from an external circuit, reactions as indicated by the following chemical equations take place.
xe2x80x83Anode reaction: H2xe2x86x922H++2exe2x88x92xe2x80x83xe2x80x83(1)
Cathode reaction: 2H++2exe2x88x92+xc2xdO2xe2x86x92H2Oxe2x80x83xe2x80x83(2)
At this time, hydrogen is transformed into a proton at the anode, moves, together with water, to the cathode through the electrolyte, and reacts with oxygen on the cathode to produce water. Thus, for the operation of the foregoing fuel cell, it becomes necessary to supply and exhaust a reaction gas such as a hydrogen gas and air, and to extract an electric current.
A separator plate for extracting an electric current from a fuel cell and for enabling the reaction gas and water to effectively flow is disclosed in, for example, Japanese Patent Application Laid-open No. Hei 3-206763 (U.S. Pat. No. 5,108,849).
FIG. 10 is a sectional view for explaining a conceptual structure of a single cell in a fuel cell disclosed in Japanese Patent Application Laid-open No. Hei 3-206763 (U.S. Pat. No. 5,108,849). In the drawing, reference numerals 1 and 2 denote conductive separator plates, 3 denotes a cathode, 4 denotes an anode, and 5 denotes an electrolyte body using, for example, a proton conductive solid polymer. The electrolyte body 5, the cathode 3, and the anode 4 constitute a single cell. Reference numeral 10 denotes a plurality of oxidant flow channels which are formed on one surface of the separator plate 1, like bellows grooves in parallel with each other, and are for supplying, for example, an air as an oxidant to the cathode 3, and 11 denotes a plurality of fuel flow channels which are formed on the separator plate 2, like bellows grooves, and are for supplying, for example, a hydrogen gas as a fuel to the anode 4.
FIG. 11 is an explanatory view showing the upper surface of the separator plate 1 in the conventional fuel cell shown in FIG. 10. Hereinafter, the explanation will be made using FIG. 10 together with FIG. 11.
Reference numeral 20 denotes a major surface of the separator plate 1, 21 denotes an electrode support portion for supporting the electrode 3 at the separator plate 1, 22 denotes an oxidant supply opening which is formed in the separator plate 1 and is for supplying air as the oxidant, 23 denotes an oxidant exhaust opening for exhausting air, 24 denotes a fuel supply opening for supplying the fuel, and 25 denotes a fuel exhaust opening for exhausting the fuel.
In the separator plates 1 and 2, the oxidant flow channels 10 and the fuel flow channels 11 are made of spaces each surrounded with a groove which is formed by cutting the major surface, and the electrode 3 or 4.
The operation of the fuel cell will be hereinafter described with reference to FIGS. 10 and 11.
The air supplied from the air supply opening 22 of the separator plate 1 is supplied to the cathode 3 while flowing through the plurality of parallel oxidant flow channels 10. On the other hand, similarly to the oxidant, the hydrogen gas is supplied to the anode 4 through the fuel flow channels 11. At this time, since the cathode 3 and the anode 4 are electrically connected to the outside, the reaction of the chemical equation (2) takes place at the side of the cathode 3, and unreacted air, nitrogen gas and water are exhausted through the oxidant flow channels 10 to the oxidant exhaust opening 23.
At this time, the reaction of the chemical equation (1) takes place at the side of the anode 4, and unreacted hydrogen gas is similarly exhausted through the fuel flow channels 11 to the fuel exhaust opening 25. Electrons obtained by the reaction flow from the electrodes 3 and 4 via the electrode support portion 21 and through the separator plates 1 and 2.
In the conventional separator plates, it is designed such that a gas flow speed is made fast so that the produced water can be exhausted. However, if one of the plurality of flow channels is blocked, it becomes impossible to generate electricity at the electrode surface for which the one of the flow channels has responsibility, so that there has been such a case that a reaction area is substantially reduced and the characteristics are lowered.
In a laminate in which a plurality of cells are stacked on each other, there has been a problem that in the case where a deficiency of fuel occurs in even one cell of the laminate, corrosion occurs in carbon as a structural member of the electrode, separator plate, or the like as shown in the following chemical equation (3), so that fatal damage is produced and efficiency of electric power generation is extremely lowered.
C+2H2Oxe2x86x92CO2+4H++4exe2x88x92xe2x80x83xe2x80x83(3)
Besides, for the purpose of unifying a reaction distribution on a cell surface, and in order to disperse a load applied to the cell surface, such a contrivance has been made that a plurality of through holes are provided in an electrode effective surface and fastening is made as disclosed in U.S. Pat. No. 5,484,666. However, since the plurality of holes are provided in the electrode, there has been such problems that a gas flow channel becomes complicated, and a surplus area loss is increased by a gas seal or the like.
The present invention has been made to solve such problems, and an object of the invention is to provide a fuel cell which has stable characteristics and produces high voltage/high output.
According to a first aspect of the present invention, a fuel cell is comprised of a laminate in which single cells each including an anode, a cathode, and an electrolyte film sandwiched therebetween, are sequentially stacked on each other through a separator plate provided with fuel flow channels for supplying a fuel fluid to the anode and oxidant flow channels for supplying an oxidant fluid to the cathode, wherein a midway portion of the flow channels of the separator plate is provided with a communicating hole communicating with the flow channels of another separator plate for the same kind of fluid, so that on the way of reactions of the fuel and the oxidant, the same kind of fluids flow into each other through the communicating hole.
According to a second aspect of the present invention, in the fuel cell of the first aspect, a cross sectional area of the flow channel at a downstream side with respect to the communicating hole in the separator plate is smaller than a cross sectional area of the flow channel at an upstream side.
According to a third aspect of the present invention, in the fuel cell of the first or the second aspect of the present invention, an area of the anode supplied with the fuel flowing through the fuel flow channels at a downstream side with respect to the communicating hole in the separator plate is smaller than an area of the anode supplied with the fuel flowing through the fuel flow channels at an upstream side.
According to a fourth aspect of the present invention, in the fuel cell of any one of the first to the third aspects of the present invention, the fuel flow channels at a downstream side with respect to the communicating hole in the separator plate are arranged on a projected surface of the oxidant flow channels at downstream region.
According to a fifth aspect of the present invention, a fuel cell is comprised of a laminate in which single cells each including an anode, a cathode, and an electrolyte film sandwiched therebetween, are sequentially stacked on each other through a separator plate provided with fuel flow channels for supplying a fuel fluid to the anode and oxidant flow channels for supplying an oxidant fluid to the cathode, wherein a shaft is inserted in a through hole provided at a centrobaric position within a surface of the electrode and passing through the laminate, an elastic body with an area of 20 to 80% of the area of the electrode is provided around the shaft, and a compressive surface pressure is applied between both end portions of the laminate with the shaft as an axis to fasten the laminate.
According to a sixth aspect of the present invention, in the fuel cell of the fifth aspect of the present invention, a midway portion of the flow channels of the separator plate is provided with a communicating hole communicating with the flow channels of another separator plate for the same kind of fluid.
According to a seventh aspect of the present invention, in the fuel cell of the sixth aspect of the present invention, the communicating hole is provided at the centrobaric position within the surface of the electrode and is made the through hole passing through the laminate.
The fuel cell of the first aspect of the present invention uses the laminate in which single cells each including the anode, the cathode, and the electrolyte film sandwiched therebetween, are sequentially stacked on each other through the separator plate.
The separator plate is provided with the fuel flow channels and the oxidant flow channels such that the fuel fluid and the oxidant fluid are supplied to the respective electrodes while flowing, and further, the midway portion of the flow channels is provided with the communicating hole communicating with the flow channels of another separator plate for the same kind of fluid.
By the communicating hole, since the same kind of fluids flow into each other on the way of reaction of the fuel and the oxidant on the electrode, even if a flow channel at either one of an inlet side and an outlet side of a confluent point is blocked, the fluid can flow through the other flow channel, so that the fuel or oxidant can be made to flow, fluctuation of cell characteristics of the laminate can be made small, and stable and high characteristics can be obtained.
In the fuel cell of the second aspect of the present invention, the cross sectional area of the flow channel at the downstream side with respect to the communicating hole in the separator plate is smaller than the cross sectional area of the flow channel at the upstream side. Thus, even if the volume of the fuel or oxidant is decreased by reactions at the downstream side, since the cross sectional area of the flow channel is small, it is possible to keep the flow rate almost equal to that at the upstream side and the flow rate of the reaction gas in the laminate can be stably kept. Thus, fluctuation of cell characteristics of the laminate can be made small and stable and high characteristics can be obtained.
In the fuel cell of the third aspect of the present invention, the area of the anode supplied with the fuel flowing through the fuel flow channels at the downstream side with respect to the communicating hole in the separator plate is smaller than the area of the anode supplied with the fuel flowing through the fuel flow channels at the upstream side. Thus, even if fluctuation in the amount of fuel exists in the laminate and a difference in concentration of fuel is produced at a former side (upstream side) of the communicating hole of the separator plate, a distribution in concentration is smoothed at the communicating hole, and at the downstream side, since the electrode area is small, the fuel flows uniformly into the laminate and stable and high characteristics can be obtained.
In the fuel cell of the fourth aspect of the present invention, for example, when the oxidant flow channels are provided on a surface of the separator plate opposite to the surface on which the fuel flow channels are provided, and the fuel flow channels at the downstream side with respect to the communicating hole in the separator plate are arranged on the projected surface of the oxidant flow channels at the downstream region (for example, an exhaust opening region of the oxidant flow channels from the separator plate), since downstream regions where the concentration of the oxidant and the fuel supplied to the cathode and the anode becomes low are coincident with each other, the amount of reaction at the downstream side is relatively decreased, so that the possibility of deficiency of fuel becomes low, and stable and high characteristics can be obtained.
The fuel cell of the fifth aspect of the present invention uses the laminate in which single cells each including the anode, the cathode, and the electrolyte film sandwiched therebetween, are sequentially stacked on each other through the separator plate. The separator plate is provided with the fuel flow channels and the oxidant flow channels such that the fuel fluid and the oxidant fluid are supplied to the respective electrodes while flowing. Further, the through hole passing through the laminate is provided at the centrobaric position within the surface of the electrode, the shaft is inserted in the through hole, the elastic body with an area of 20 to 80% of the area of the electrode is provided around the shaft, and a compressive surface pressure is applied between both end portions of the laminate with the shaft as an axis to fasten the laminate. Thus, it is possible to uniformly apply a ring-shaped surface pressure to the effective surface of the electrode surface.
In the fuel cell of the sixth aspect of the present invention, the separator plate is provided with the fuel flow channels or oxidant flow channels such that the fuel or oxidant flows and is supplied to the respective electrodes, and the midway portion of the flow channels is provided with the communicating hole communicating with the flow channels of another separator plate for the same kind of fluid. The ring-shaped surface pressure is uniformly applied to the electrode surface, and the fluid can flow together with the same kind of fluid in another separator plate in the laminate, so that fluctuation of cell characteristics of the laminate is small, and stable and high characteristics can be obtained.
In the fuel cell of the seventh aspect of the present invention, the communicating hole is provided at the centrobaric position within the surface of the electrode and is made the through hole passing through the laminate. Since the hole for the fastening shaft and the communicating hole can be made the same, the structure becomes simple.